Haemodynamic and hormonal changes in pregnancy
The increased haemodynamic demands of pregnancy are significant, and they start early: cardiac
output rises by 50% by the middle of the second trimester, and it must be maintained throughout the
rest of the pregnancy (Fig. 2) [3]. Any condition that limits the ability to increase cardiac output will
result in pregnancy being poorly tolerated. During labour, cardiac output increases further due to
increased heart rate from pain and anxiety, and uterine contractions returning blood to the venous
system. Blood pressure and oxygen requirements also rise during contractions. Following delivery,
uterine and placental auto-transfusion and release of caval compression result in a significant increase
in the venous return. The changes associated with pregnancy can take several weeks to return to normal. Patients with impaired ventricular function therefore remain at risk for several weeks after
delivery, and many cases of pregnancy-associated cardiomyopathy are not revealed until several weeks
later.